Cannot get noise free realistic render in blender cycles
1. Read: 7 Ways to Get Rid of Fireflies Once and For All

List of the techniques explained in the article:


Use Bigger Light Sources
Use Bigger Shadow Sizes
Use "Multiple Importance Sampling" for HDRs
Use 'Filter Glossy'
Check "No Caustics"
Use "Clamping"
More Samples


2. Read: Using Portals to Accelerate your Render Times

For an interior scene such as yours, Portals can make a big difference. Portals tell Blender to only channel the environment lighting through a specific area (like a window), which makes for faster, cleaner renders.

3. Learn about the new Denoising feature.

Grab the latest version of Blender (currently 2.79 Release Candidate 2). This includes the new Denoising feature, which works wonders. So after you have done Step 1 and optimized your settings, this is how you can really polish it all up.

※ Note that if Progressive Refine is enabled, Denoising options will be grayed out. Learn more